Dental Materials Exam 1
Ask the patient to breathe through their nose and move their head forward. Also, do not over fill the tray
What steps can be taken to avoid the gag reflex?
hydration
When mixed with water, the hemihydrate is converted back to dihydrate
ZOE and plaster
Which of the following dental materials are no longer used when taking impressions?
mechanical properties
Which type of property do these fall into? elasticity, stress, strain, poisson's ratio, resilience, toughness, fracture toughness, fatigue, creep, stress relaxation, stress concentration
physical properties
Which type of property do these fall into? electrical conductivity, abrasion resistance, solubility, water sorption, color, interaction of materials with x-rays
24 hours
hydration reaction completed, gypsum fully set
hygroscopic expansion
if the gypsum becomes immersed into water or comes in contact with water while setting the gypsum will take-up additional water; swells
elastomer
impression material that has high degree of accuracy, used for impressions for crowns
condensation silicone
impression material that is very hydrophobic, must be poured immediately, usually has many voids; used for crown and bridge work mainly, but also for partial dentures, implants and overdentures; set time 5-7 min
reversible hydrocolloid
impression material used for crowns, requires special equipment, water cooled trays, can be softened and reused
mucostatic
impression taken without displacing any tissue; gets all the detail of the mucosa
crown
indirect restoration replacing individual teeth
activator paste
inert oil (forms a paste) sulfur (facilitates the reaction) lead oxide (causes polymerization and cross-linking)
fluctuating dipole
intermittent, uneven distribution of electrons around the atom or molecule
die
is a positive reproduction of a single tooth
study model cast
is a positive reproduction of both maxillary and mandibular, is a positive reproduction of the hard & soft tissues of the oral cavity
microleakage
leakage of fluid and bacteria caused by microscopic gaps that occur at the interface of the tooth and the restoration margin
polymer
long chain covalent bonds; many varieties of plastics; some have cross-linked bonds between chains (ex. dental composites)
calcium sulfate dihydrate
main component of gypsum, still contains water content
density
mass of material/object in a given volume; measured density = gm/cm3 higher density/heavier atom
potassium sulfate
material added to gypsum that acts as an accelerator
colloid
material consisting of two or more substances in which one substance does not go into solution but is suspended within another substance
ultimate strength
maximum amount of stress a material can withstand without breaking
coefficient of thermal expansion
measure of change in volume in relation to change in temperature; cold causes restorations to shrink; heat causes restoration to expand
fracture toughness
measure of energy required to fracture a material when a crack is present; glass and porcelain - low; metal - high
electrical conductivity
measured by performing a pulp test; the metal of the amalgam in the restoration conducts heat with another metal object
tensile strength
measures the force required to pull something such as rope, wire, to the point where it breaks
hysteresis
melting point much higher than boiling point, and gelling at mouth temperature; body temp. of patient is different from temp. of material
one minute
mixing time for alginate
impression compound
mixture of 3 constitutes
ceramics
mostly ionic bonds; strong when compressed; brittle and weak when pulled apart
metals
mostly metallic bonds, some ionic and covalent; proportions determine type of characteristics; properties do not change when bent or manipulated
percolation
movement of fluid in the microscopic gaps of the restoration margin as a result of differences in expansion and contraction rates of the tooth and restoration with temperature changes; the process of heating and cooling and the accompanying opening & closing the gap; causes microleakage within restorations
Goldilocks Principle
not too hard, not too soft, just right
covalent bond
occurs between 2 atoms; two atoms share two (a pair of) electrons
permanent dipole
occurs when the shared electron in a covalent bond are not shared equally; partially charged; form weak bonds
ionic bond
one electron is given up by an atom and accepted by another
base paste
polysulfide (forms rubber on polymerization) filler (gives body) plasticizer (control viscosity)
nonaqueous elastomeric impression materials
polysulfide, silicones, polyethers, addition silicones
wetting
preparing the surface of a material so that a chemical or micromechanical bond can occur; depends on the angle of the liquid to the material
thermal conductivity
rate of heat flow through a material
Poisson's Ratio
ratio of the strain in the direction of the stress to the strain in the direction perpendicular to the stress elastic pulling/release
dry strength
reached in 24-hours, water has evaporated , 2X as great as wet strength
indirect restoration
restorations fabricated outside the mouth and then placed into the cavity preparation
direct restoration
restorations placed directly into the cavity prepartion
composite
restorative material that is a combination of 2 or more different materials ex. polymer + ceramic = fiberglass
polysulfide material
rubber base impression material, used for dentures, special spatula, long working time 4-6 minutes
abrasion resistance
scratch or wear resistance of the material; follows Goldilock's Principle
3-4 minutes
setting time of alginate
diatomaceous earth
silica, inert filler used in alginate; Gives the material 'body'
creep
small change in shape of an object when it is under continuous compression; slow process that occurs around restorations; can be caused by temperature fluctuations
hydrogen bond
special case of permanent dipole due to the fact that H+ has only one electron
disinfect, rinse, store in ziplock with mouthwash and water
steps of disinfecting and cleaning of dentures:
primary bond
strong bonds, either ionic, covalent, or metallic bonds
positive reproduction
study model/cast of oral structures
restoration
term use to describe the material used as the replacement of lost tooth structure
pontic
term used to describe that part of a fixed bridge replacing missing tooth/teeth; no tooth structure present; the teeth between the two abutments
viscosity
the ability of a material to flow
compressive strength
the force per unit area that an object can withstand when compression
stress
the force that develops in an object
proportional limit
the greatest stress a structure can withstand without permanent deformation
imbibition
the opposite of syneresis
water sorption
the property of a material to absorb water, material swells increasing in size; weight gained when soaked in water
hardness
the resistance of a solid to penetration
setting expansion
the slight swelling of the gypsum while it is getting hard, crystals push against each other creating porosities
force
the weight also referred to as a load: ie: loading the implant - placing the crown on the implant
implant
titanium screws that are placed in the jaw and replace missing teeth
19-24mL / 100g
water to powder ratio for high-strength stone
45-50mL / 100g
water to powder ratio for plaster
30mL / 100g
water to powder ratio for stone (1st mix)
27-28mL / 100g
water to powder ratio for stone (2nd mix)
secondary bond
weaker bonds; also called van der Waals forces; develop from partial charges from an uneven distribution of electrons around an atom or a molecule
glutaraldehyes isophores sodium hypochlorite synthetic phenols dual or synergized quaternaries sodium bromide and chlorine (not usually used on impressions)
what are some acceptable disinfectants?
crusing strength
what it takes to break up ston
atomic bonding
what type of bonding happens when teeth bite together?
hemihydrate
when gypsum becomes powder is it a hemi- or di- hydrate?
abutment
when placing a fixed bridge, the tooth the crown is attached to, root of the tooth still present
stress concentration
when stress increases around defects; Area or point of significantly higher stress associated with a structural discontinuity
1800s
which century were these materials popular in? amalgam porcelain crowns and inlays
20th
which century were these materials popular in? cast metals polymers
1700s
which century were these materials popular in? gold, ivory, porcelain tooth shapes wax and gypsum zinc oxide for fillins and cements
glutaraldehydes
which disinfectant should never be sprayed since it is an extremely toxic as an aerosol?
initial setting time
working time, loss of gloss of gypsum becomes semi-hard, 5-7 minutes
zoe
zinc oxide and eugenol impression material; used for denture final impression; no longer used for this purpose
addition silicone
AKA vinyl polysiloxanes; impression material used for crowns, comes in two tubes or a gun and cartridge; set time 6-8 min
positive
Pouring an impression is a ________ reproduction of the patient's teeth
Seat tray is posterior to anterior. When removing tray, place one hand on the tray handle and rock the tray to loosen. One can also place one finger on the posterior aspect of the tray to help release the suction
What is the proper technique for seating and removing impressions?
Baseplate wax and elastomeric materials
What materials are used to take a bite registration?
Reversible hydrocolloids (agar), plaster, wax, zinc oxide & eugenol (ZOE), polysulfides (rubber base), condensation silicones, polyethers, additional silicone
What other impression materials are available?
gel; sol
A hydrocolloid's natural state is a ____, but on heating becomes a ____.
stress
Compression, tension, shear, torsion, and bending are all types of __________.
1/2
The width of the base should be _____inch wider than the widest part of the dental arch
imbibition
Water may be absorbed causing the impression to swell
ionic, covalent, metallic
What are the 3 primary atomic bonds?
permanent dipoles, hydrogen bons, and fluctuating dipoles
What are the 3 secondary atomic bonds?
Potassium alginate, diatomaceous earth (inert filler), calcium sulfate (reactor), sodium phosphate (retarder), and antimicrobials
What are the components of alginate?
brinell, knoop, rockwell, and vickers
What are the four hardness scales used in dentistry?
Righties — 7:00 Lefties — 5:00
What are the proper patient and clinician positioning for taking mandibular impressions?
Righties — 11:00 Lefties — 1:00
What are the proper patient and clinician positioning for taking maxillary impressions?
Add rope wax and/or soften with hot water
What can be done to adapt an impression tray for proper fit?
Try a different tray size or place rope wax around the tray
What can be done to allow the tray to be seated successfully?
take a bite registration
What can be done to ensure that the study casts are an accurate representation of a occlusion?
an allergic reaction
What could be causing the itchiness and difficulty swallowing?
Tray size is wrong and the mandibular tori is present
What could cause the difficulty in seating the mandibular tray?
the manufacturer's directions
What direction should you follow when handling dental materials?
The temperature of the water. If it is too hot, it will set too quickly. If it is too cold, it will set slowly
What effects the setting time of alginate impression material?
Not all the material will be removed and it creates a mess
What happens if the material is removed prior to setting?
A recording of the relationship between the maxillary and mandibular arches. It records the patient's natural bite
What is a wax bite registration?
A soften wax is placed over to cover mandibular teeth, then ask patient to close their mouth
What is the procedure for taking a bite registration?
inelastic impression materials
compound, plaster, ZOE, wax, hydrocolloids
galvanic shock
electrical current that occurs between to dissimilar metals
metallic bond
electrons are shared by all of the atoms
toughness
energy absorbed in an object up to the failure point on of stress/strain causing distorting or fracturing
fatigue
failure of object after repeated stress over time
final setting time
from start of mix to rigid mass that can be separated from impression, minimum 1-hour/safe to separate, not fully set
wet strength
from start of pour to one hour after, water still present
exothermic reaction
gives off heat as it set or gets hard
nuclei of crystallization
Crystals of gypsum form in clusters, branching from a common center called the growth and interlocking of these crystals contributes to strength, rigidity and dimensional change
look in the patient's mouth
How do you determine the proper size of the impression tray?
1 hour
How long should one wait before separating the casts?
fixed bridge
Indirect restoration that replaces multiple teeth (minimum of 3 teeth) with crowns
atomic bond
Bonds resulting from electromagnetic force (EM); negative and positive; attract or repel
24 hours
Casts should be stored for how long before trimming?
undercure; overcure
For light activated materials, you can _______ and cannot _______.
strain
Force or stress occurs in an object that opposes the stress placed on an object
negative
The alginate impression is a ___________ reproduction of the patient's teeth.
calcination
The process whereby water is lost when gypsum is heated during manufacturing
Medical Device Amendment of 1976
This calls for classification, safety and efficacy of medical devices. ex. Class 1 - least regulated (toothbrushes) Class 2 (composites and amalgam) Class 3 - most regulated (implants)
dental cements
Used glue things together
syneresis
Water exudes (releases) causing the impression contracts
elasticity
a change in shape of a material when compressed or stretched and the ability return to original shape
dental impression material
a class 2 device composed of materials such as alginate or polysulfide intended to bee placed on a preformed impression tray and used to reproduce the structure of a patient's teeth and gums. Device is intended to provide models for study
stiffness
a material's resistance to deformation
vapor pressure
a measure of a liquid's tendency to evaporate and become a gas; lower pressure/longer vaporization
Class II Restoration
a posterior restoration that includes any combination of the mesial, distal, occlusal surfaces of the tooth; ie MO, DO, MOD
Class I Restoration
a restoration that includes a combination of occlusal, buccal, and or lingual surfaces to the tooth; ie O, L, B, OL, OB. OLB
Class V Restoration
a restoration that includes only the cervical 1/3rd of the tooth
Class VI Restoration
a restoration that includes only the direct cusp tip of the tooth
stress relaxation
a slow decrease in force over time; object returns to state of equilibrium
slurry
a thin mixture of gypsum or other material
resilience
ability of a material to absorb energy and not become deformed
aqueous elastomeric impression materials
alginate and agar
irreversible
alginate is an example of what kind of hydrocolloid?
solubility
amount of a material that dissolves in a liquid
heat of vaporization
amount of energy need to boil a material
heat of fusion
amount of energy needed to melt a material
heat capacity
amount of heat a material can hoard, store up; amount of energy needed to raise the temperature of 1 unit of mass by 1 degree Celsius
Class III Restoration
an anterior restoration that includes any combination of the mesial, distal, lingual, buccal surfaces; does not include the incisal edge of the tooth; ie ML, MB, DL, DB, MLD, MBD, DLB, MDLB
Class IV Restoration
an anterior restoration that includes any combination of the mesial, distal, lingual, buccal surfaces; including the incisal edge of the tooth; ie MIL, MIB, DIL, DIB, MDIL, MDIB, DILB, MDILB ....
negative reproduction
any impression, prior to being poured
boiling and melting points
atomic bonds broken by thermal energy
gypsum
calcium sulfate hemihydrates; reacts with water to form hard mass of calcium sulfate dihydrate
sodium phosphate
common additive to alginate that acts as a retarder to slow down working time
borax
common additive to gypsum acts as a retarder
Gilmore needle
device used to determine setting time of gypsum
10 minutes
disinfection time of alginate impression
